Various technologies have now been developed for applying thin films to substrates used in manufacturing semiconductor devices. Among the more established techniques is Chemical Vapor Deposition (CVD). Atomic Layer Deposition (ALD), a variant of CVD, is a relatively newer technology now emerging as a potentially superior method of achieving highly uniform, conformal film deposition. ALD, although a slower process than CVD, has often demonstrated an outstanding ability to maintain ultra-uniform thin deposition layers over complex topology. This is at least partially true because ALD is not as flux dependent as is CVD. This flux-independent nature of ALD allows processing at lower temperatures than with conventional CVD methods.
ALD processes proceed by chemisorption at the deposition surface of the substrate. The technology of ALD is based on concepts of atomic layer epitaxy developed years earlier for growing polycrystalline and amorphous films of zinc sulfide, for example, and dielectric oxides for electroluminescent display devices. The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD appropriate reactive precursors are alternately pulsed into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas, e.g. Ar, purge. Each precursor injection provides a new atomic layer additive to previously deposited layers to form a uniform layer of solid film. The cycle can be repeated until the desired film thickness is attained. Thus, the introduction of the gas Ax is followed by introduction of a gas By to form a layer of AB material. This process of introducing Ax and then By can be repeated a number of times to achieve an AB film of a desired thickness.
While ALD typically allows for the formation of high quality, uniform films across a wide array of surface topologies, problems can still arise. In general, deposition initiation, i.e. formation of the first layer or few layers, is often the most problematic stage of film formation with ALD. In the preceding example, for instance, the subgroup x on the Ax gas can be a large, bulky molecule which can sterically hinder the formation of a continuous monolayer. In addition, the chemisorbent nature of Ax may be such that while it adheres adequately to the underlying substrate, it can adsorb to other materials and thereby interfere with the subsequent reaction of compounds utilized to form succeeding layers.
What is therefore needed in the art is a new method of ALD which overcomes the disadvantages associated with this deposition technique. Also needed is a new film composition for use on a wide array of substrates in semiconductor devices.
The invention provides a method of depositing a film on a substrate in a semiconductor device. Using ALD process conditions hereinafter described, the substrate is first exposed to at least one adherent material in a quantity sufficient for the material to adhere or adsorb onto the surface of the substrate and thereby form an initiation layer over the substrate. The initiation layer presents at least one first reactive moiety which is then chemically reacted with at least one first reaction material to form a second reactive moiety. The second reactive moiety is then chemically reacted with at least one second reaction material so as to form a reaction layer over the initiation layer. The initiation layer is not substantially degraded during formation of the reaction layer, and together with the reaction layer can constitute the final film. Additional reaction layers may also be formed over the initiation layer, and all these layers together will then constitute the final film.
In a further aspect of the invention, there is provided a film suitable for use on a substrate in a semiconductor device. The film has an initiation layer of an adherent material, and one or more reaction layers formed over the initiation layer. Each of the reaction layers may be comprised of a metal or metal-bearing compound.
Additional advantages and features of the present invention will become more readily apparent from the following detailed description and drawings which illustrate various embodiments of the invention.